North Korea Cuts Off the Remaining Military Hot Lines With South Korea

North Korea cut off the last remaining military hot lines with South Korea on Wednesday, accusing President Park Geun-hye of South Korea of pursuing the same hard-line policy of her predecessor that the North blamed for a prolonged chill in inter-Korean relations.

Amid tensions over the North’s third nuclear test last month and ensuing United Nations sanctions, North Korea had already shut down Red Cross hot lines with South Korea and a communication line with the American military command in South Korea. But the North’s decision to cut off military hot lines with South Korea on Wednesday was taken more seriously in Seoul because the two Koreas have used those four telephone lines to control daily cross-border traffic of workers and cargo traveling to the North Korean border town of Kaesong.

The two countries run a joint industrial park at Kaesong, the last symbol of inter-Korean cooperation that has survived the political tensions of recent years. Seoul officials said 887 South Korean workers were in Kaesong on Wednesday. The traffic was running normally on Wednesday and Thursday morning, with long lines of trucks crawling through the border crossing, South Korean officials said, indicating that the North Korean military did not go so far as to stop cross-border economic exchanges.

“There do not exist any dialogue channel and communications means between the D.P.R.K. and the U.S. and between the North and the South,” said a North Korean statement sent to the South Korean military by telephone and later carried by the North’s official Korean Central News Agency. “Not words but only arms will work on the U.S. and the South Korean puppet forces.”

D.P.R.K. stands for the Democratic People’s Republic of Korea, the North’s official name.

The North’s action came a day after its top military command ordered all of its missile and artillery units to be on “the highest alert” and ready to strike the United States and South Korea. It also vowed to take “substantial military actions” to retaliate against joint United States-South Korean military drills, which involved American B-52 bomber sorties over South Korea.

The last time North Korea severed all military hot lines, during joint United States-South Korean military drills in 2009, it allowed an inter-Korean economic liaison office in Kaesong to serve as a communication channel with Seoul, and South Korean workers could commute to Kaesong. The two Koreas continue to maintain hot lines between their civil aviation authorities.

“Under the situation where a war may break out any moment, there is no need to keep North-South military communications,” the North said on Wednesday.

The North Korean action came shortly after the South’s president, Ms. Park, stressed both firmness and reciprocity in her nation’s policy toward the North.

“If North Korea provokes or does things that harm peace, we must make sure that it gets nothing but will pay the price, while if it keeps its promises, the South should do the same,” Ms. Park said during a briefing with her government’s top diplomats and North Korea policy makers. “Without rushing, and in the same way we would lay one brick after another, we must develop South-North relations step by step, based on trust, and create sustainable peace.”

Her new unification minister, Ryoo Kihl-jae, South Korea’s point man on North Korea, later told reporters that his government was willing to consider lifting trade embargoes imposed on the North after the deadly sinking of a South Korean Navy ship in 2010, but not before North Korea takes responsibility for the sinking, which killed 46 South Korean sailors.

Seoul blamed a North Korean torpedo attack, but the government in Pyongyang insists that it had nothing to do with it.

“We keep our door open for dialogue,” Mr. Ryoo said.

But on Wednesday, the Committee for the Peaceful Reunification of Korea, the North Korean counterpart to Mr. Ryoo’s ministry, berated Ms. Park for warning a day earlier that the Pyongyang government could ensure its survival only when it stops building nuclear weapons while its people go hungry.

“This time her remarks have gone beyond the line,” the committee said.

It said Ms. Park’s recent comments were “utterly shocking” compared with her earlier indications that she would not maintain the hard-line policy of her predecessor, Lee Myung-bak, whom she replaced on Feb. 25.

“If she keeps to the road of confrontation like traitor Lee, defying the warnings of the D.P.R.K., she will meet a miserable ruin,” the committee said.

Also Wednesday, the North’s main ruling-party newspaper, Rodong Sinmun, said it planned “substantial military actions,” including “pre-emptive nuclear strikes” against the United States and South Korea.

Despite its successful launching of a three-stage rocket in December, however, “North Korea doesn’t have the capability to carry out this latest threat to attack U.S. bases” in Hawaii, the United States mainland and Guam using long-range missiles, said James Hardy, the Asia Pacific editor for IHS Jane’s Defense Weekly.

The Pentagon recently announced that it would ramp up its missile defense on the West Coast and Alaska, citing the threat of North Korea’s KN-08 missiles, which were unveiled during a military parade in Pyongyang last April.